People in the modern society often obtain much information by viewing various kinds of matter (It is possible, for example, to obtain much useful information by viewing a subway map, a sign, various kinds of web pages existing on the internet, recognize that a tomato is ripe by viewing the color of the tomato, and check doneness of broiled meat by viewing it.) and soothe their heart (For example, people soothe their heart by viewing a scene with full of bloomed flowers or mountains with leaves turned red and yellow.).
Such viewing is of course to recognize various kinds of things by eyesight and it is important whether the things themselves (contour) can be seen or not in the visual perception (It usually depends on whether the eyesight is good enough or not. Hereinafter, it is referred to as “shape perception”.) as well as whether color differences can be discriminated or not (It usually depends on the chromatic vision. Hereinafter, it is referred to as “color perception”.). For example, in one of the above examples, each subway route is often drawn in a different color in the subway map in order to discriminate each route, but it becomes difficult to recognize each route by each color if the number of routes to be shown is increased (For example, a subway map around Tokyo area may be a good example.). In the example of the subway map, the color perception is more important than the shape perception. And the color perception is also more important than the shape perception in the case of checking how ripe the tomato is by viewing the color of the tomato or checking the doneness of the meat by viewing the color of the meat. Also, the color perception is more important than the shape perception in the case of finding a flower when such a flower blooms in a gorgeous color in the hedge with full of leaves and twigs, viewing leaves turned red, or the like.
In such cases where the color perception is more important than the shape perception, the color deficient observer may not render the perception well by eyesight if the color perception is necessary since the color deficient observer has a lower level of the color perception than people who have no color deficiency (Herein after, referred to as “color non-deficient observer”.). The color deficiency is caused by a disorder of cones as photoreceptor cells of the retina and categorized in a red-green color blindness such as a protan (protanopia and protanomaly) having disorder in L-cone cell characterized by a peak of sensitivity in a longer wavelength zone and a deutan (deuteranopia and deuteranomaly) having disorder in M-cone cell characterized by a peak of sensitivity in a middle wavelength zone, and a blue-yellow color blindness such as a tritan (tritanopia and tritanomaly) having disorder in S-cone cell characterized by a peak of sensitivity in a shorter wavelength zone. In the case where these three cone cells are deficient, the color deficiency is a total color blindness. However, the total color blindness is quite rare and most color deficiencies are the red-green color blindness, to which it is said that 5% of Japanese men and 0.2% of Japanese women belong. In order to enhance the color perception of such a color deficient observer, a filter for the color deficient observer to drive a car and lenses of eyeglasses for the color deficient observer and so on have been developed (For example, patent references 1 and 2 should be referred to.), but many color deficient observers have a resistance to using the filter or lenses having a thick coloring or a special reflecting film such that they are not widely used.
Recently, an image processing technology utilizing a computer is also developed. For example, converting colors difficult to percept into colors easy to percept by an image processing method or the like, and inputting lines between colors are also considered. However, it is possible for people having red-green blindness to discriminate two colors as different colors by utilizing these methods, but it is not understood which tomato is ripe, red and ripe tomato or green tomato, although the red and ripe tomato and the green tomato can be discriminated as different tomatoes. Therefore, the technology can not be applied to various situations.